SCHMITTERITE-A NEW URANYL TELLURITE from MOCTEZUMA, SONORA Rrcnano V

THE AMERICAN MINERALOGIST, VOL.56, MARCH-APRIL, 1971

SCHMITTERITE-A NEW URANYL TELLURITE FROM MOCTEZUMA, SONORA Rrcnano V. GarNrs

AssrRnct

A new mineral, uranyl tellurite UOiTeO3, has been found at the Moctezuma Mine, Moctezuma, Sonora. The mineral is pale straw yellow in color and occurs in minute rosettes of micaceous crystals, usually associated with emmonsite. It is orthorhombic, space group Pmab with a 7sffi, b 10.089, and c 5.363 A; there are four foimula units per ceII, 11:1; G:6.878 (meas), 6.916 (calc). The mineral is biaxial negative with indices above 2.00. Principal powder lines are 3.682 (10), 5.35 (9),3.099, (9),4.73 (8), 3.170 (8), and t.971 (7). The name is for Eduardo Schmitter V. of the University of Mexico'

INrnooucrroN While studying the Moctezuma tellurium-gold deposit in 1961, an unidentified light yellow mineral was noted in small tufts and micaceous scales growing on emmonsite. Subsequent study at the Instituto de Geologia showed that this mineral was new and consisted of uranium, lellurium, and oxygen only. The description of this mineral was delayed becauseits scarcity and the lack of measurablecrystals made a complete description difficult to achieve. These problems were finally solved, and the name schmitterite is now proposed for this species.

OccutnBNcp Schmitterite was found at the Moctezuma Mine, Moctezuma, Sonora, along with a number of other new oxy-salts of tellurium (Gaines, 1965). In the great majority of samples of schmitterite that have been collected the mineral is sparingly scattered on knobs or typical groups of curved fibers of emmonsite, or is on limonite surfaces adjacent to emmonsite encrustations. The schmitterite may occur as single crystals or grains, or more commonly as small rosettes rarely exceeding1 mm in diameter. The groups of crystal blades making up these rosettes are so thin and plastic that they smear or disintegrate when touched with a needle. Another less common form of occurrenceis scattered on quartz frac- ture surfaces with crusts of small crystals of moctezumite, sometimes pseudormorphously replacing the latter. In such instances it has a glistening, micaceous appearance. The total amount of mineral found, thinly scattered on matrix, was probably not over two grams. Only one specimen collected from the San Miguel prospect showed 4tt 412 RICHARD V. GAINES

schmitterite, which was thickly scattered on a druse of mackayite crystals.

Cururcar PnopBnrrps X-ray fluorescenceanalysis on schmitterite showed only uranium and tellurium to be present. The mineral when heated to 600oC shows no change in appearanceand a weight loss of less than 1 percent, hence it is assumedto be anhydrous. Schmitterite is readily soluble in dilute hydro- chloric acid and in alkalis. rnsufficient pure natural material was avail- able for chemical analysis, for which reason it was necessary to synthesize the mineral to get enough material for this purpose. It proved relatively easy to synthesize schmitterite but difficult to prepare a product absolutely free from extraneous phases.One method of synthesis used with considerable successwas to heat a mixture of TeOs and UOs.HrO in 1:1 stoichiometricproportions in water solution to a temperature ranging from 1000 to 400oC. Because of the high pressure this reaction was carried out in vycor tubes in a stainlesssteel bomb. The product was a slurry of fine crystals of UOz.TeOa, often contaminated with a little tetragonal TeOz (synthetic paratellurite). Varying the temperature up to 400oC seemed to make little differencein the size of crystals produced, which were usually lessthan 50 microns in size. Only one run, in which the vycor tube ac- cidentally broke within the bomb, produced some coarse crystals up to 3 mm long mixed with iron oxides and other extraneousproducts. Synthesis was also carried out at room temperature using the method of Khodadad (1962), giving a pure product which was, however, even finer in grain size than the high temperature product. Analysis of the synthetic product gave 63.48 percent UOa and 36.95 percent TeO2, total 100.43 percent. This compares with 64.19 percent UOs and 35.81 percent TeOz theoretical for UOz.TeOe. The powder photograph of this product matched that of natural schmitterite, there- fore the chemicalformula of schmitteriteis UOz.TeOs.

Cnvsrar Grolrprny Single crystal X-ray studies were made with both Weissenbergand Buerger precession cameras, using filtered copper radiation. Natural crystals were unsuitable for this work, since their small size and extreme thinness caused them to bend upon the slightest contact. However, one lot of synthetic crystals gave individuals of sufficient size to permit handling and resulted in excellent photographs. Extinctions observed were as follows: 200 present when h is even, SCHMITTERITE

T.q.ere1. X-n.ly Pomnr Dara, or Scnarrrrrnrrl' Cu ReorerroN, Nr Frr-rpn

d(calc.) d(obs.) I d(calc.) d(obs.) I A A (vis. est ) A A (vis. est.)

001 J.JOJ J.5.) 9 003 1.788 1.788 I o20 5.045 s.03 z 42r r.734 1.734 5 011 4.736 4.7s 8 242 r.664 r.666 2 r20 4.246 4.25 I 061 1.605 1.604 I 111 4.056 4.06 z 223 1.549 1.549 6 200 3.930 3.933 z 422 1.512 1.5r2 L 021 s.675 3.682 10 Ml r.489 1.489 2 121 3.329 3.324 1. 043 1.459 1.459 20r 3.170 3.170 8 004 1.341 1.340 1 220 3.100 3.099 9 1s3 1.3t9 1.318 L 2tt 3.O24 3.025 522 1.310 1.305 z 031 2.U9 2.850 I 54r 1.295 1.292 z 221 2.684 2.686 + 253 1.266 1.266 I 012 2.592 2.594 I 461 1.243 1.242 1 040 2.522 2.525 3 263 1.169 1.r70 3 tt2 2.461 2.466 1 244 | 134 1.134 2 022 2.368 2.365 4 273 1.079 1.080 1 202 2.215 2.214 J 373 1.031 1.032 1 212 2.164 2.r58 a 391 |.012 1.012 I 032 2.097 2.093 J 1.10.0 1.001 1.001 I 1?'.) 2.026 2.026 A 241 1.974 1.971 7 5rz r.842 1.843 4 4tL 1.815 1.815 T

0fr0 present when ft is even, 2ft0 present when ft is even, Z0l present when /zis even, hkl-no extinctions. Schmitterite is orthorhombic, sp-acegroup Pmab with @7.860t.004, D 10.089+.002,and c 5.363*.002 A. The cell volume is 425.31A3, and Z:4. photographs Powder of schmitterite give a pattern -in which the three strongestIines correspondto 3.675,5.363 and 3.100 A. Forty-four lines were measured;a complete list of spacingsis given in Table 1. Whenever possible,single crystal intensities were used to help with the indexing of Iines that could be ascribed to more than one reflection.

Cnvsrlr Monprrorocv The crystal habit of schmitterite is blade-like, with elongation parallel to a and the width parallel to b. The thickness of the blades, which in natural material is probably 2 pm or less,is in the c direction. The most 4t4 RICHARD V, GAINES prominent form is 001. Becuaseof the thiness of the blades morphological measurementscould not be made, but several prisms, domes, and pyra- mids could be seen upon microscopic examination of synthetic crystals. The only cleavage observed is taken as (100) with reference to the conventionally chosenorthorhombic cell in which the long dimension of the blade like crystals is o, their wide dimension is 6.

Puvsrclr, Pnopnnuns Color. Schmitterite varies from colorlessto light yellow, the most common color being a very pale straw yellow. Synthetic schmitterite is pale creamy yellow. The luster is pearly.

Hardness.Schmitterite is very soft, with a hardnessprobably close to 1 on Moh's scale. Testing of hardness is uncertain because the minute scalesare so exceedinglythin that they break or bend when the slightest pressureis exertedon them.

Specif.c Gravity. It was not possible to isolate a sufficiently large pure sample of natural schmitterite for specific gravity determination. After the mineral was synthesized., it was finally possible to make a gravity determination on a 1.00-gram sample of finely crystalline synthetic material. This material gave an X-ray powder pattern identical to that of the natural mineral with only a few extra faint lines caused by a trace of contaminating tetragonal TeOz. The resulting specifi.cgravity of 6.878 (average of two determinations) is in good agreement with the theoretical 6.916 calculated from the cell volume and contents, although it is appreciably lower than the 7.57 reported by Khodadad (1962) on artifical UOr.TeOa.

Opti.calProperties. Schmitterite is biaxial negative, with 2V near 75o. It shows parallel extinction but no discernible pleochroism. X: c (the acute bisectrix), Y:b, and Z:a.0:2.05 using Cargilleliquids. 7)2.11, probably near 2.15. a could not be measured becausethe thinness of the crystal blades in relation to their width made observation of the Becke line difficult, particularly in conjunction with the dark-colored index liquids. The optic orientation was determined in the universal stage.

TypB SpncrupNs Samples of schmitterite have been deposited at the rhuseum of the Institute of Geology and at the Smithsonian Institution of the U. S. National Museum, Washington,D.C., under specimennumber NMNH t22475. SCHMITTERITE 415

NauB The name schmitterite is in honor of Professor Eduardo Schmitter Villada, for more than 35 years Professorof Mineralogy and Petrology at the National University of Mexico and also ResearchPetrologist at the Mexican Institute of Geology at the University. The mineral and name schmitterite have been approved by the Committee on New Minerals and New Mineral Names of the International Mineraloqical Association. Acrnowr,rocmNrs Most of the work on schmitterite was done at the Instituto de Geologia oI the National University of Mexico, Guillermo P. Salas, Director, and the writer wishes to express his appreciation to Ing. Salas for his sponsorship of this work. He also lvishes to thank Quim. Alberto Obregon who made the chemical analysis; Dr. Gabrielle Donnay of the Geophysical Laboratory, who checked the X-ray single crystal workl to Dr. Maria Luisa Crau,'ford of Bryrr Mawr College, who determined the optical constants of schmitterite; and to D. C. Appelman and Judith Konnert for help in computer refinement of the unit celi dimensions.

RelnnrNcns

GatNts, R. V. (1965a) Mineralizacion de telurio en Ia mina Moctezuma, cerca de Mocte- zuma, Sonora. Unit. Nac. Autonoma Mer., Inst. Geol,.Bol.75' (pt. 1). - (1965b) Moctezumite, a new lead uranyl tellurite. Amu. MineraL. 50' 1158-1163. Knooale.o, M. P. (1962) Sur Ie tellurite neutre d'uranyle (UOr) (TeO) C. R. Acail. Sci. P ari,s (Fronce) 255, 1617-1618.

Manuscript receioed.,Moy 3, 1970; occepteilJor publicati'on, November 7, 1970.